The present invention relates to a large burner, particularly for liquid fuels (light, medium and heavy oils), with a fuel supply pipe, concentrically located in an air supply pipe and partially enclosed by a sleeve carrying air, with atomizer jet (spray diffuser) and a swirl (twist) producing body enclosing the fuel supply pipe upstream of the spray diffuser; the swirl producing body comprises a fixed blower wheel and receives combustion air from the periphery, with the combustion air quantity regulatable upstream of the burner head as a function of the prevailing fuel flow. Burners of this type are known from British Pat. No. 945,880 and German Laid-Open Document No. 1,501,904.
The spray diffusers of such large burners have the form of control jets (nozzles). Upstream of the discharge of these control nozzles is a turbulence chamber to which the oil is supplied tangentially. In the direction of the spray diffuser axis is a bore (drill hole) which serves to return the fuel not needed with partial load. As a result, the relatively small fuel quantity flowing out during partial load operation flows out at a relatively large angle, e.g., 100.degree.-120.degree. and forms a solid mist whose droplets are relatively small. The fuel quantity is under a relatively large pressure, e.g. of 30 bars. During partial load operation, the major part of the fuel quantity delivered to the turbulence chamber is returned (fed back) under a relatively low pressure, e.g., of 6 bars so that the fuel quantity remaining in the turbulence chamber circulates in it at a relatively high swirl (twist) speed so that this relatively large diffuser angle results. Since the fuel droplets are relatively small, they relatively quickly assume the speed of the combustion air so that they participate in this rotating motion of the air if the combustion air is supplied with twist (swirl). Due to this twisted air, an underpressure region forms in the spray diffuser area, leading to a return flow of the gases in the direction toward the oil mist so that its speed is braked. This oil mist is moved outside which, during its combustion, leads to coke deposits on the mixer device surfaces enclosing the spray diffuser. Therefore, previous metal surfaces (British Pat. No. 945,880) were replaced by a muffle (flame tube) (German Laid-Open Document No. 1,501,904) which comes to glow during burner operation in order to burn the coke deposit formed.
If one switches from partial load to full load operation, the major portion of the fuel quantity supplied to the turbulence chamber (for heavy oil), or the entire fuel quantity is sprayed via the spray diffuser of relatively small cross-section into the combustion chamber, requiring a relatively high static pressure in the turbulence chamber. Since in this case there results a relatively small difference between the pressure ahead of and the pressure in the turbulence chamber, the circulating speed of the oil in the turbulence chamber is much smaller than when operating on partial load. Accordingly, there results a smaller diffusion angle and the size of the fuel droplets increases. This increases the dwell time, necessary for complete combustion of the fuel particles, in the combustion chamber, requiring relatively large combustion chambers.
From the above it follows that the above-mentioned large burners work perfectly in full-load operation because the required dwell time is sufficient, while in partial load operation the returning gases carrying the fuel mist droplets to the forward surface of the mixing device and cause there coke deposits.
It is, therefore, an object of the present invention to generate a flow directed against the emitted oil mist, this flow being proportional to the nozzle output (droplet size), to brake the oil droplets as far as necessary, and to increase their dwell time in the combustion chamber so that complete combustion is achieved.
Another object of the present invention is to provide an arrangement of the foregoing character which is substantially simple in construction and may be economically fabricated.
A further object of the present invention is to provide an arrangement, as described, which may be readily maintained in service and which has a substantially long operating life.